Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. Referring now to FIG. 1, the head disk assembly 100 includes at least one disk 102 (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor 104 for rotating the disk, and a head stack assembly (HSA) 106. The spindle motor typically includes a rotating hub on which disks mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host. The head stack assembly 106 typically includes an actuator, at least one head gimbal assembly (HGA) 108 that includes a head, and a flex cable assembly 110.
During operation of the disk drive, the actuator must rotate to position the heads adjacent desired information tracks on the disk. The actuator includes a pivot bearing cartridge 112 to facilitate such rotational positioning. One or more actuator arms extend from the actuator body. An actuator coil 114 is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. A crash stop is typically provided to limit rotation of the actuator in a given direction, and a latch is typically provided to prevent rotation of the actuator when the disk dive is not in use.
In magnetic and optical disk drives, the head typically comprises a body called a “slider” that carries a magnetic transducer and/or focusing lens. Magnetic transducers typically comprise a writer and a read element. A magnetic transducer's writer may be of a longitudinal or perpendicular design, and a magnetic read element may be inductive or magnetoresistive. In a magnetic and optical disk drives, the slider is typically supported in very close proximity to the magnetic disk by a hydrodynamic air bearing. As the motor rotates the disk, the hydrodynamic air bearing is formed between an air bearing surface of the slider of the head, and a surface of the disk. The thickness of the air bearing at an important location on the slider (e.g. the location of the transducer) is commonly referred to as “flying height.”
Magnetic hard disk drives are not the only type of information storage devices that have utilized air bearing sliders. For example, air bearing sliders have also been used in optical information storage devices to position a mirror and an objective lens for focusing laser light on the surface of disk media that is not necessarily magnetic.
The flying height is a key parameter that affects the performance of an information storage device. Accordingly, the nominal flying height is typically chosen as a careful compromise between each extreme in a classic engineering “trade-off.” If the flying height is too high, the ability of the transducer to write and/or read information to/from the disk surface is degraded. Therefore, reductions in flying height can facilitate desirable increases in the areal density of data stored on a disk surface. However, the air bearing between the slider and the disk surface can not be eliminated entirely because the air bearing serves to reduce friction and wear (between the slider and the disk surface) to an acceptable level. Excessive reduction in the nominal flying height degrades the tribological performance of the disk drive to the point where the disk drive's lifetime and reliability become unacceptable.
One challenge that disk drive engineers face is to maintain the desired nominal flying height nearly constant despite changes in radial positioning of the head. As the radial position of the head changes, the relative velocity of the disk surface due to disk rotation also changes. Specifically, the relative velocity of the disk surface increases with increasing radius, tending to influence the flying height to increase as the slider is radially positioned towards the disk outer diameter. We may refer to this as the “velocity effect” on flying height.
Furthermore, as the radial position of the head changes, the relative direction of incoming air flow changes. Specifically, in disk drives that utilize a rotary actuator (or a linear actuator having a line of action that does not pass through the disk center) the skew of the slider will change as the actuator changes its radial position relative to the disk surface. As the skew of the slider changes, the direction of incoming air flow relative to the slider changes accordingly, tending to change the flying height. We may refer to this as the “skew effect” on flying height.
In the past, disk drive engineers have invented various different methods and/or air bearing features to at least partially cancel the velocity effect on flying height with the skew effect on flying height. For example, engineers have designed disk drives so that the maximum skew will occur at the disk outer diameter (where the disk surface velocity is highest)—partially canceling the two effects. Also for example, so-called Transverse Pressure Contour air bearings have utilized recessed steps along the outer edges of the air bearing side rails to better pressurize the rails when the incoming air flow was significantly skewed.
Air bearing designers have also tried skewing the shape of the trailing pad of certain air bearing designs, and/or one or more pressurizing steps around the trailing pad of certain air bearing designs, to better cancel the skew effect and velocity effect. However the design of the air bearing trailing pad, and/or pressurizing steps adjacent the trailing pad, strongly influences other important flying height sensitivities such as sensitivity to changes in ambient pressure (i.e. altitude sensitivity) and sensitivity to slider or disk crown and camber. These sensitivities strongly depend upon the trailing pad design because the trailing pad typically includes the location where the maximum pressure developed by the air bearing occurs, and the trailing pad is also where the flying height is most important because the trailing pad is typically adjacent the transducer (if any). Therefore it is desirable for engineers to have ample freedom to design the trailing pad, and/or pressurizing steps adjacent the trailing pad, to reduce or practically minimize flying height sensitivity to changes in altitude, crown, and/or camber, rather than being constrained to focus the trailing pad design on canceling the skew effect and velocity effect.
Accordingly, what is needed in the art is an air bearing design feature that enhances cancellation of the disk velocity effect (on flying height) with the skew effect (on flying height), without overly constraining the design of the trailing pad and/or pressurizing steps adjacent the trailing pad.